This invention relates to a telecommunications system, and to a method of operation thereof. More particularly, the invention relates to a telecommunications network using Internet Protocol (IP), and specifically to a system for handling emergency calls in such a network.
In mobile communication systems, there are situations in which a call request may not be allowed. For example the user may not have paid a bill, or the mobile system may have no information at all about the user, or there may be congestion on the network, or the mobile phone may be reported stolen.
In the GSM system, emergency calls may be allowed even when one of these factors apply.
It is expected that 3rd generation (3G) mobile phones will allow voice over IP. That is, the Internet Protocol (IP) will be used for the whole call from the mobile phone to the network gateway which is the connection to the public switched telephone network (PSTN) which includes the emergency services operator. Therefore, all calls will send the voice signals as packet data, rather than as circuit switched data.
The document xe2x80x9cGSM on the Netxe2x80x9d, by Granberg, Ericsson Review No. 4, 1998 pages 184-191, describes a voice over IP system, based on the recommendation ITU H.323. The H.323 protocol separates call control (signalling in the call setup phase) from connection control (the actual data flows).
However, it provides no mechanism to allow for special treatment of emergency calls.
The present invention is concerned with allowing special treatment of emergency calls, so that such a call can be successful even though another voice call would not be allowed.
According to one aspect of the invention, a mobile communication device analyses a dialled number and, in the case of an emergency call, sends a session activation request which includes an emergency call indication.
According to another aspect of the invention, a node in a packet data communication network detects an emergency call indication in a session activation request, and allows call setup, even though a call without such an indication would fail.
According to another aspect of the invention,